Optical aligning device



Aug. 7, 1951 E. A. FONTAINE OPTICAL ALIGNING DEVICE Filed March 7, 1950 2 Sheets-Sheet 1 fl MICROJCOPE EMILE A. FONTAINE INVENTOR WJ-hw I WWW ATTORNEYS E. A. FONTAINE OPTICAL ALIGNING DEVICE Aug. 7, 1951 Filed March '7. 1950 2 Sheetsheet 2 EMILE A. FONTAINE INVENTOR ATTORNEYJ Patented Aug. 7, 1951 OPTICAL ALIGNING DEVICE Emile A. Fontaine, Gethsemane, Ky., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application March 7, 1950, Serial No. 148,236

3 Claims.

This invention relates to optical aligners which are instruments for the accurate determination of a straight line.

It is an object of the invention to provide an optical aligner of simple construction but extreme accuracy.

It is also an object of the invention to provide such an instrument which does not require any reticle mark and which does not easily get out of adjustment.

According to the invention an optical aligner is made up of an objective, which may be a concave mirror but which is preferably a positive lens, for forming an image of a test object which may be in any form and may include a scale. Semitransparent plane reflectors are provided in both focal planes of the objective. In the case of a concave reflector, the two focal planes are coincident and hence a single mirror is used as the semi-transparent reflecting means. In the case of a positive lens, two separate semi-transparent mirrors are used, one in the front focal plane and the other in the rear focal plane immediately in front of the above mentioned image. This combination of semi-reflecting means and objective causes the formation of a second image superimposed on the first, but inverted relative thereto. An optical system such as a microscope is provided for viewing the superimposed images.

The optic axis of the objective is perpendicular to both of the plane mirrors in the positive lens embodiment and is perpendicular to the one mirror which constitutes both semi-reflecting means in the case of the concave mirror embodiment. The optic axis is the aligning axis of the instrument.

Although it is not essential to the invention, it is sometimes desirable to provide light deviating means to permit fine adjustment of the instrument. This may conveniently take the form of a tilting plate or rotatable wedges somewhere in the optical beam, but any of the light deviating devices commonly used in range finders are satisfactory. Other advantages of the invention will be apparent from the following description when read in connection with the accompanying draw.- ing in which:

Fig. 1 is a schematic view of a simple optical system incorporating the invention.

Fig. 2 is a diagram illustrating the operation of Fig. 1.

Fig. 3 is a side elevation, partly in section of an optical aligner according to the invention.

Fig. 4 shows the field of view seen through this instrument.

Fig. 5 illustrates the optical system for another embodiment of the invention.

Fig. 6 illustrates schematically the operation of the aligner.

In Fig. 1 light from an object I0 as indicated by a light ray II is refracted by a positive lens I2 to form an image Id at the point I5 on the optic axis of the objective. Accordin to the invention, a semi-transparent reflector I6 positioned in the back focal plane of the objective I2 reflects part of the light as indicated by the ray I! back toward the lens I2 which again refracts it to form ray I9. A second semi-transparent reflector 2| located in the front focal plane of the -objective I2 reflects this light as indicated by ray 22 as if it were coming from the same point on the object I0 as does the ray II. This ray 22 is again refracted by the lens I2, as indicated by the my 23 to form a second image 24 at the point I4. This second image is inverted relative to the image I4 and is not as bright as the image I4. Incidentally any of the ray 23 reflected at the surface I6 can make a similar trip through the lens twice to reinforce the image [4.

Reference to Fig. 2 will illustrate why the image .24 is superimposed on the image I 4 rather than being formed somewhere else. The distances from the object In to the focal plane 2| and from the focal plane I6 to the image I4 are labeled A and B in Fig. 2. By simple optical principles A.B=F When the ra I3 is reflected at the mirror I6, it crosses the optic axis at the point I8 whose distance from the focal plane I6 is also 13, or more precisely is minus B. The ray I'I traveling from the point I 8 to the lens I2 is refracted by the lens so that the ray I9 appears to come from a point 35. That is, the lens I2 forms a virtual image 32 of the real image 3| which is formed at the point I8 by light reflected by the mirror I 6.

Since the object 3I is at a distance minus B from the focal plane I6, the virtual image 32 must be at a distance minus C from the focal plane 2I where C=A. This is true because both of the following relationships hold.

with respect to object I0 and image I4, A.B=F With respect to object 3| and image 32, C.B=F Thus C=A.

The reflector 2| receiving the ray I9, apparently from the image 32 reflects it as if it came from a virtual-image 33 at the same distance from the mirror 2| as is the image 32. Thus the virtual image 33 is located at the same point as the original object J0. Thus it is that ray it! appears to come from the object I0 and hence when refracted by the lens l2 it will come to focus once again at the point I5. However, the virtual image 33 is inverted relative to the object l and hence the second image 24 formed at the point is inverted relative to the first image I4.

The superimposed images thus formed are viewed through a microscope 26 by the eye 21 of an observer.

In Fig. 3 the housing 40 of an optical aligner includes a hollow cylinder in which a lens mount 4! is held by suitable set screws. This lens mount 4| includes an internal thread into which a lens rim 42 is screwed carrying lens elements 43 which constitute a B-piece telescope objective covering only a relatively narrow field. However the specific coverage is not a critical part of the invention, nor is the particular type of positive lens. In Fig. 3 the lens elements 43 are cup centered by spacing rings 44 and clamping rings 46 which concentrically engage the refractive surfaces of the elements. At each end of the lens mount 4|, a glass plate 48 is mounted in screw rings 49 which permit adjustment of the distance of the plates 48 from the lens system. The inner surfaces of the plates 48 are provided with semi-reflecting surfaces in the manner common to beam splitters. The outer surfaces of these plates and the surfaces of the lens elements are preferably provided with reflection reducing coatings such as magnesium fluoride, one quarter wave length thick. During manufacture the lens is first mounted near the center of the lens mount 4| and then the plates 48 are inserted and adjusted until the semirefiecting surfaces are accurately in the focal 1 planes of the lens.

The images formed by this system are viewed by a microscope 54 provided with an adjustable eyepiece 52 and focused in the usual manner by a focusing knob 53. The whole instrument is provided with three-point suspension on studs, two of which are indicated at 54, and which are preferably glass or Carboloy lapped to or to a knife edge.

Preliminary aiming of the device is provided in this embodiment by a simple gunsight consisting of fiducial marks 50 which are lined up with the target as in aiming a gun. Low power telescopic gunsights will also serve for preliminary aiming.

Since it is sometimes desirable to make a fine adjustment after the preliminary aiming without moving the whole instrument, a light deviating means is provided, consisting of two wedges 60, which rotate about the optic axis of the system in opposite directions. The wedges are carried in bevel gears 6| which engage a small bevel gear 62 which in turn is adjustable by means of a knob 63 on the outside of the instrument. The whole mount 64 is also rotatable in the housing 40 to permit the fine adjustment to be made in any azimuth. Any light deviating device of the types used in rangefinders, is suitable for this purpose, such, for example, as the tilting plate shown in my co-filed application Serial No. 148,237.

When one views an object through this instrument, the field of view is similar to that shown in Fig. 4 in which the ima e ll appears to one side of the point 13 which corresponds to the aiming or aligning axis of the instrument. A second ima e. 12 appears on th opp si s de of the point 73 and at the same distance there from. If the device is to point at some particular a I, i v

4 part of the object, adjustments are made until the two images of this part are in register.

In Fig. 5, a different embodiment of the invention is shown in which the objective consists of a spherical concave mirror H. In the case of a concave mirror the two focal planes are coincident and hence only one semi-transparent mirror serves to provide both reflections required by the invention. In this figure light from the object 15, after passing through a lens element such as the Schmidt aspheric plate 76 (or a concentric meniscus element of known type) for correcting the spherical aberration of the concave mirror, is brought to focus by the concave mirror 1'! to form an image 18. A semitransparent reflector 8| positioned in the focal plane of the mirror reflects part of this beam to form a ray 82 which is again reflected by the mirror 11 to form ray 83 and then reflected a second time at the plane mirror 8| to form a ray 84 apparently coming from the same point of the object 15. This ray 84 is then reflected a third time by the mirror 11 as indicated by ray 85 to form a second image 85 superimposed on. and inverted relative to, the image 18.

While the Schmidt plate 16 and the mirror 11 may be said to have an optic axis, the factor which preciseiy defines the optic axis of this instrument is the orientation of the mirror 8| relative to the concave surface Ti. As shown in the drawing, the optic axis is constituted by the line which passes between the point of the mirror 8| which is at the greatest perpendicular distance from the sphere represented by the surface 11. This line passes through the focal point of the mirror 71 and is perpendicular to the mirror 8|. It is thus a very precisely defined optic axis. This point does not come up in the case of a positive lens since the optic axis of the latter is always well defined whereas a concave spherical mirror does not have a precise optic axis until it is combined with some other element. However, the surface 8! must be orthogonal to the optic axis, whatever system is used. A small prism 9!) reflects the light from the images 18 and 86 into a microscope 9! for viewing by the eye 92 of an observer.

In this embodiment, preliminary aiming is conveniently provided by a small prism 81 which reflects light directly from the object to a low power wide field telescope 88, the eye of the observer being held at 89 for such aiming.

In Fig. 6, the aligner shown in Fig. 3, is used for testing the flatness of a long surface 95. To do this, a target 96 which may be a unit associated with the surface such as a carriage riding on a track or which may be a special target placed on the surface 95 just for the alignment test, is examined by an observer :(whose eye is at 98) through the aligner 40. The aligner and target are adjusted relative to one another until in perfect alignment. The target is then moved to different positions indicated at 91 and the discrepancy from perfect alignment is noted. The curvature of the sur-. face 95 is greatly exaggerated in the picture, but in practice the aligner is used to pick up variation of a thousandth of an inch in tracks supposedly flat for twenty feet or more.

The invention is not limited to these embodiments but is of the scope of the, appended claims.

I claim:

1. An optical aligner comprising an objective 75 for forming an image of a test object, plane semi-reflecting means in the focal planes of the objective orthogonal to the optic axis of the objective whereby a second image is formed superimposed on and inverted relative to the first and means for viewing the superimposed images.

2. An optical aligner comprising a positive lens for forming an image of a test object, two semi-transparent plane reflectors orthogonal to the optic axis of the lens system and respectively in the front and rear focal planes of the lens system for forming in cooperation with the lens system a second image superimposed on and inverted relative to the first image, and means for viewing the superimposed images.

3. An optical aligner according to claim 2 including light deviating means aligned with the lens system to permit fine adjustment of the alignment.

EMILE A. FONTAINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Number Name Date 1,199,307 Risley Sept. 26, 1916 2,395,605 Young Feb. 26, 1946 FOREIGN PATENTS 15 Number Country Date 269,447 Germany Jan. 22, 1914 64,842 Austria May 11, 1914 360,996 Germany Oct. 9, 1922 

